1. Technical Field
The present invention relates to an image forming apparatus and an image forming method that develops an electrostatic latent image with toner by using a toner carrying roller having a surface on which periodic concave-convexes are disposed.
2. Related Art
Recently, developing devices for developing an electrostatic latent image carried on an image carrier with toner and image forming apparatuses having the developing devices in which a toner carrying roller that is formed in an approximate cylinder shape and carries toner on the surface is disposed to face an image carrier have been widely used. The applicant of this application, in order to enhance the characteristics of toner that is carried on the surface of the toner carrying roller, has disclosed an image forming apparatus, which employs a toner carrying roller in which convex portions that are regularly disposed on the surface of the roller formed in a cylinder shape and concave portions that surround the peripheries of the convex portions are disposed, in advance (see JP-A-2007-233195 (FIG. 6)). Under such a structure, the concave-convex patterns formed on the surface are managed to be uniform, and accordingly, there is an advantage that the thickness, the charged amount, or the like of a toner layer that is carried on the surface of the roller can be controlled in an easy manner.
On the surface of the toner carrying roller, the toner is mainly carried in the concave portions. Thus, the toner carrying roller has a relatively small effective surface area that contributes to transport of the toner, for example, compared to a toner carrying roller having a surface that is blast processed. Even when a height difference of the concave-convex is configured to be large for supplementing a decrease in the amount of transport of the toner accompanied with the small effective surface area of the toner carrying roller, toner that is carried in a deep portion of the concave portion cannot easily contribute to a developing process, and thereby the efficiency of the developing process is not sufficient. Accordingly, there is a case where the density of an image to be formed is insufficient.
As described above, in the image forming apparatuses and the image forming methods that use the toner carrying roller having the surface on which regular concave-convexes are disposed, for acquiring sufficient image density, the toner carried in the toner carrying roller should be effectively contributed to the developing process so as to increase the efficiency of the developing process.